1. Technical Field
The invention relates to an etching method, and more specifically to a method of etching a to-be-processed object made of silicon.
2. Background of the Art
In recent years, with an increase in the degree of integration of semiconductor devices, dimensions of individual elements have been decreasing. Accordingly, a high aspect ratio (depth of a trench (or a via hole)/diameter of the trench (or the via hole)) is required for trenches (grooves) or via holes (holes) formed in a silicon substrate in order to ensure element isolation and memory cell capacitor area.
Conventional methods of forming trenches or via holes in a silicon substrate include a method in which the silicon substrate is etched using fluorine radicals produced by forming a plasma of a fluorine-containing gas. In this case, since the reaction of fluorine radicals and silicon spontaneously proceeds, etching at room temperature is isotropic. Accordingly, a method has been employed in which after the silicon substrate is etched to form part of the trenches or the via holes, a protective film is formed on sidewalls thereof, and then etching is further performed (e.g., see Patent Document 1).